Abstract
Due to the generality and flexibility of Monte Carlo method in geometric modeling, Monte Carlo method plays an important role in accurate simulation of random media. At present, rand om sequential addition method (RSA) and distinct element method (DEM) are more accurate and mature explicit modeling methods. The former approach has the problem of upper limit of packing fraction, which is suitable for stochastic geometry with lower filling rate. DEM method can fill random medium model with packing fraction higher than 60%, but DEM is not suitable for non-contact dispersed particles based on the interaction between particles. There fore, an improved DEM method is proposed to solve the problem of modeling non-contact p articles dispersed in the stochastic media with high packing fraction. The virtual surfaces are constructed outside of the outer layer of particles to make them in contact with each other. Thus, the particle system is suitable for DEM method. The construction of virtual surface does not affect the neutron transport process. The correctness of the improved DEM is verified by comparing the total filling particle number and calculation results ofkeffwith RSA method. At the same time, according to the distribution of filling particles, the improved DEM method fills the particles more uniformly.
Highlights
After the Fukushima Daiichi nuclear disaster, the need for secure nuclear reactors seems to be more important than ever
Random sequential addition method is a kind of efficient filling method compared to the distinct element method (DEM) method
rand om sequential addition method (RSA) method has up limitation of packing fraction, and this upper limit value has been studied in this work
Summary
After the Fukushima Daiichi nuclear disaster, the need for secure nuclear reactors seems to be more important than ever. Taking the advantages of the flexible geometry modeling and the use of continuous-energy nuclear cross sections, Monte Carlo (MC) codes play an important role in the accurate simulation of stochastic medium [2]. Implicit methods cannot obtain right packing fraction This phenomenon has been observed in stochastic medium packing fraction tests using Reactor Monte Carlo code (RMC). As for the explicit modeling methods, two main accurate and mature approaches have been applied in PBR simulation, random sequential addition method (RSA) and distinct element method (DEM). RSA method samples the location of particles one by one with no overlap, the filling process does not need any dynamic calculation and much quicker than DEM method. An improved DEM method is proposed to solve the problem of modeling non-contact particles dispersed in the stochastic media with high packing fraction.
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